descktopCapture stream is mono

[jmcker]

Stream received via navigator.mediaDevices.getUserMedia is mono (possibly with additional filtering).

Current constraints:

const mediaStreamConstraints = {
    audio: {
        mandatory: {
            chromeMediaSource: 'desktop',
            echoCancellation: false,
            googEchoCancellation: false,
            googAutoGainControl: false,
            googNoiseSuppression: false,
            googHighpassFilter: false,
            googTypingNoiseDetection: false,
            googAudioMirroring: false,
            googAudioMirroring: false,
            googNoiseReduction: false,
        }
    },
    video: {
        mandatory: {
            chromeMediaSource: 'desktop'
        }
    }
};

This could be a general limitation or related to: w3c/mediacapture-main#457

[jmcker]

This ended up being an issue with some part of how Chrome's was handling SDP settings on the actual WebRTC connection rather than the local stream. The commit here allows munging the SDP to force stereo.